The present invention relates to a method and a system for control of an intake air throttling valve fitted to the intake manifold of a diesel internal combustion engine, and, more particularly, relates to a method and a system for control of an intake air throttling valve fitted to the intake manifold of a diesel internal combustion engine, for throttling down the flow of air into the combustion chambers through said intake manifold of the engine, in order to raise the temperature of the exhaust gases of the engine so as to purge or rejuvenate a soot particle catcher of a per se well known sort fitted to the exhaust system of the engine by heating said particle catcher up and by combusting a soot particle accumulation in said soot particle catcher by igniting it by heating it by said raised temperature of said exhaust gases of the engine.
Nowadays, it is common and conventional to provide a soot particle catcher to the exhaust system of a diesel engine. Such a soot particle catcher catches and accumulates carbon particles and other solid particles present in the exhaust gases of the diesel engine, and prevents their escape to the atmosphere. Since it is becoming more and more understood nowadays that fine soot particles such as carbon particles may present a significant health hazard to the public, the provision of such a soot particle catcher to the exhauat system of a diesel engine is very important from the environmental and public health point of view.
Such a soot particle catcher normally has a filter like structure for catching the soot particles, and as a matter of course this filter structure inevitably tends to become clogged up, over a long period of use of the soot particle catcher, with an accumulation of soot particles, chiefly carbon particles. When this happens, not only does the efficiency of the soot particle catcher for purifying the exhaust gases of the diesel engine of soot particles drop drastically, but also the resistance of the soot particle catcher to the flow therethrough of exhaust gases increases, which deteriorates the actual operation of the diesel engine, causing its breathing efficiency to drop, which causes a loss of engine power. This has presented a serious problem with regard to such a soot particle catcher; either it has been necessary to regularly remove the soot particle catcher in order to cleanse it of soot particles which have become accumulated therein, requiring dirty, expensive, and troublesome works; or some system has had to be provided for cleaning or purging or rejuvenating the soot particle catcher in situ, without removing said soot particle catcher from the engine.
One way in which it is possible to purge or rejuvenate such a soot particle catcher is by burning out the combustible soot particles such as carbon particles which are clogging the filter structure of the soot particle catcher by increasing the temperature of the exhaust gases passing through the soot particle catcher above the ignition temperature of said combustible soot particles. This is possible and practicable because the filter element which traps said soot particles may typically be constructed of a refractory material which is substantially unaffected during such combustion.
During operation of the diesel engine, when the load on the diesel engine rises to a high load level wherein the excess air ratio in the exhaust gases becomes small, it is quite possible for the temperature of the exhaust gases passing through the filter structure of the soot particle catcher to spontaneously rise above the ignition temperature of the soot particles clogging the soot particle catcher, without the provision of any special means for raising the temperature of said exhaust gases. In this case, purging or rejuvenating of the soot particle catcher as described above may spontaneously occur, by burning out said soot particles lodged therein as a clogging accumulation. However, this spontaneous self purging or rejuvenating process cannot be relied upon. Diesel engines, especially in automotive vehicles, are only irregularly operated in high load conditions; and when an automotive vehicle is being operated in urban traffic it is quite unusual for the diesel engine thereof to be operated in the high load operational region. Thus such spontaneous self purging or rejuvenating of a soot particle catcher, if relied upon, might not occur in time to purge or rejuvenate the soot particle catcher before its clogging had unacceptably deteriorated the functioning of the diesel engine to which it was fitted. Therefore, if this form of purging the soot particle catcher by burning out the soot particles accumulated therein is to be practiced, it is necessary to practice some particular special and reliable method for raising the temperature of the exhaust gases of the diesel engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof, in order reliably to purge or rejuvenate said soot particle catcher whenever it becomes clogged.
As per se well known prior art method for raising the temperature of the exhaust gases of a diesel engine to a tempearture higher than the ignition temperature of the soot particles which are becoming lodged in the soot particle catcher thereof in order to purge or rejuvenate said soot particle catcher has been to reduce the amount of excess air which is being supplied to the combustion chambers of the diesel engine during operation of said diesel engine, by limiting the air intake of the engine. This raises the temperature of the exhaust gases of the engine because the hot gases produced by combustion of the fuel which is injected into the combustion chambers of said engine to be burnt therein is mixed with a lesser amount of cool air, i.e. of excess air.
This limiting of the air intake of the diesel internal combustion engine has been heretofore implemented by the provision of an intake air throttling valve at an intermediate position in the air intake passage, or the air intake manifold, of the diesel engine. When it is decided that the soot particle catcher requires to be purged or rejuvenated by raising the temperature of the exhaust gases passing therethrough to higher than the ignition temperature of the carbon particles lodged therein, so that the intake air throttling valve is required to be positioned to its position in which it substantially throttles the flow of air through the intake manifold in order thus to heat up the temperature of the exhaust gases, and then the air pressure in the air intake manifold of the diesel engine downstream of this intake air throttling valve becomes as a matter of course depressed below atmospheric pressure. In this case, if this throttling of the air intake passage is performed to too great an extent, then the operability of the diesel engine is severely deteriorated, its performance and power output suffer, and the drivability of a vehicle incorporating said diesel internal combustion engine will become poor. In particular, there is a risk of misfiring of the diesel internal combustion engine, if said depression in the air intake manifold of the diesel engine downstream of said intake air throttling valve becomes too great. Further, when the depression in the intake manifold is too large, this can cause emission of quantities of black smoke in the exhaust of the diesel internal combustion engine. This of course is quite unacceptable on environmental grounds, and in view of the standards for control of noxious emissions in the exhaust gases of internal combustion engines for vehicles, which are becoming more and more severe nowadays. In this regard, the inventor of the present invention has found, through investigations of operation of the diesel internal combustion engines under the throttling of the flow of air through the intake manifold in order to raise the temperature of the exhaust gases, that if the depression in the air intake manifold of the diesel engine downstream of said intake air throttling valve is held not to be greater than some certain predetermined value (the actual value of which depends upon the design of the diesel internal combustion engine), irrespective of the load on and the revolution speed of the engine, the abovementioned troubles caused by the limitation of the intake air flow can be clearly avoided.